We cloned two homeobox genes, Emx1 and Emx2, related to empty spiracles, a gene expressed in very anterior body regions during early Drosophila embryogenesis, and studied their expression in mouse embryos. Emx1 expression is detectable from day 9.5 of gestation whereas Emx2 appears to be already expressed in 8.5 day embryos. Both genes are expressed in the presumptive cerebral cortex and olfactory bulbs. Emx1 is expressed exclusively there, whereas Emx2 is also expressed in some neuroectodermal areas in embryonic head including olfactory placodes in earlier stages and olfactory epithelia later in development.

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We isolated and mapped the human homeobox gene EVX1. This gene encodes a protein of 407 amino acid residues containing a homeodomain closely related to the Drosophila even-skipped (eve) segmentation gene of the pair-rule class. EVX1 belongs to a small family of vertebrate eve-related homeobox genes including human EVX1 and EVX2 genes, their murine homologs, Evx 1 and Evx 2, and the frog Xhox-3 gene. We previously reported that EVX2 is localized at the 5' end of the HOX4 locus on chromosome 2. We show here that EVX1 is localized at the 5' end of the HOX1 locus on chromosome 7, 48 kb upstream from the most 5' of the eleven HOX1 genes, namely HOX1J. Both EVX genes are transcribed in an opposite orientation as compared to that of adjacent HOX genes. Human HOX1 and HOX4 complex loci appear to be both closely linked to a homeobox gene of the EVX family.

The recently identified placenta growth factor gene (PIGF) code for a protein related to the vascular permeability factor (VPF). We present evidence indicating that expressing of this gene could be regulated at the post-transcriptional level. The region upstream to the coding region of PIGF mRNA contains a small open reading frame (ORF), potentially coding for a peptide of 15 amino acids. The translation of different constructs in reticulocyte and wheat germ lysates as well as in COS-1 and CV-1 cells indicates that this short region is a translational inhibitory element since mutations in its two potential initiator codons increase PIGF synthesis in vivo. Using RNAse protection assay, we demonstrate that the PIGF mRNAs obtained from human term placenta and JEG choriocarcinoma cell line have a complete 5' untranslated region and, consequently, also the above mentioned small ORF. Finally, the analysis of a bovine PIGF genomic clone reveals that this small ORF is strongly conserved with respect to both putative peptide sequences and distance from the PIGF coding region.

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